Medivh (WoW)

Magus or Magna Medivh was the last Guardian of Tirisfal. From birth, he was corrupted and possessed with the spirit of Sargeras, who planned to use Medivh to conquer Azeroth. It was Medivh who contacted Gul'Dan and opened the Dark Portal, letting the Orcs into Azeroth. He was slain by Lothar, only to return shortly before the Third War to act as a Prophet to guide the Orcs, Humans, and Elves to unity against the Burning Legion.